PHASE-SEPARATION IN POLYMER-SOLUTIONS AND GELS

A brief overview of the kinetics of phase separation in polymer solutions and gels is presented. Small angle light scattering measurements of the time evolution of the structure factor following a quench into the spinodal region for polystyrene cyclohexane solutions show several unusual features as compared to either polymer blends or simple binary liquid mixtures. Nonlinearities appear to be important right from the beginning and the scaling behavior in the intermediate stages indicates the formation of ramified domains. The mobility varies with time, so that the phase separation process slows down as time proceeds. Similar experiments in gelatin solutions in a mixture of water and methanol show the effects of simultaneous occurrence of phase separation and gelation. The most dramatic effect is the pinning of the phase separated morphology at some intermediate stage in the unstable region of the phase diagram upon gelation. The final domain size depends strongly on the quench temperature.